Introduction
Suicide is the tenth leading cause of death in the United States; during 2013 more than 41,000 individuals died as a result of self-inflicted injury, a
rate of 13 suicide deaths per 100,000 individuals1. The rate of suicide among the 22 million veterans in 2013 was almost three times the rate in the
general population2. Several investigations have demonstrated an association between suicide and traumatic brain injury (TBI)3. TBI—a type of acquired brain injury that occurs as a result of a blow, jolt, or bump to the head or a penetrating injury that disrupts brain function4—has been diagnosed among more than 333,000 service members since 20005. Repeated traumatic brain injury (rTBI) can result in damage to the cerebral axons and lead to symptoms such as impaired judgment and impulse control, memory loss, confusion, aggression, and depression6.

A study assessing TBI among veterans engaged with homeless services programs provided by United States Department of Veterans Affairs (VA) found that 47% had a probable TBI which is almost 4 times the rate of TBI among the general population7. While research has addressed the relationship between TBI and suicide, as well as TBI and homelessness among veterans generally, no research has examined suicide risk in veterans with TBI who are also experiencing homelessness. Given the fact that veterans comprise 11% of the adult homeless population in the United
States8, and have high rates of suicidal ideation and suicide attempts9, as well as TBI, this is not a trivial gap in current understanding. This study aimed to understand the associations between suicide risk and physical, psychological, social and military characteristics among veterans with TBI who are experiencing homelessness.

Materials & MethodsSample
The study sample included 103 veterans who presented for homeless outreach services between December 2010 and September 2011 at either a
VA medical center or a drop-in center for veterans experiencing homelessness and who screened positive for TBI on two instruments, described below. An additional 19 veterans were determined ineligible for the study because they did not screen positive for TBI on both instruments; 84.4% of all participants were retained in the sample.

MeasuresDemographic information. Basic demographic information included race, education, marital status, military branch and rank, and experience of
deployment and combat.

TBI-4 Questionnaire. This 4-question brief screen assessed history of TBI among veterans accessing VA homeless services. A positive response to any of the following items indicated TBI: (1) Have you ever been hospitalized or treated in an emergency room following a head or neck injury? (2) Have you ever been knocked out or unconscious following anaccident or injury? (3) Have you ever injured your head or neck in a car accident or from some other moving vehicle accident? 4) Have you ever injured your head or neck in a fight or fall?

Ohio State University TBI Identification Method (OSU TBI-ID). The OSU TBI-ID is a structured interview designed to elicit self-report of a TBI occurring over a person’s lifetime with a focus on (1) injuries caused by a blow to the head or high-velocity forces; (2) altered consciousness; (3) treatment received; and (4) sequelae. Information is obtained on the number of injuries, severity of injuries, initial and persistent sequelae and age at time of injury. The present study assessed the following variables from this instrument: mean number of TBIs, veterans’ TBI experience—whether the veteran experienced loss of consciousness (LOC), being dazed/confused without LOC and amnesia without LOC—and TBIrelated symptoms such as headache, dizziness, ringing in ears, fatigue and sleep problems, blurred vision, temper and irritability, inability to manage stress, issues with memory and problem-solving and seizures. Scores from this instrument have a reliability between 0.84–0.93.

MINI International Neuropsychiatric Interview (MINI).
The MINI is a psychiatric interview that assesses a number of psychiatric disorders including mania/ hypomania, major depressive episode, panic disorder, agoraphobia, anxiety disorder, post-traumatic stress disorder (PTSD), alcohol/substance abuse and dependence and psychotic disorders. The MINI has a reliability of 0.76–0.93, a sensitivity between 0.46– 0.94 and a specificity between 0.72–0.97, depending on the subscale.

The MINI also assesses suicide risk with a subset of 15 questions from which a total risk score can be computed: 1–8 indicates low risk, 9–16 moderate
risk, and 17 or greater high risk. Suicide-related items include: feelings of hopelessness, thoughts of being better off dead, thoughts of hurting oneself,
thoughts/plans about suicide or history of a suicide attempt. We dichotomised risk for suicide as no/ low/moderate versus high risk. There were no
substantial differences in demographic and mental health characteristics between those with no, low or moderate risk for suicide.

Procedure
To participate in the study, veterans had to be at least 18 years of age and seeking homeless services through the local VA medical center. A psychology
technician employed by VA administered each of the measures described above; veterans who were not found to screen positive for TBI, on both the TBI-4 and the OSU TBI-ID, were excluded. This study was approved by the Institutional Review Boards of the University of Pennsylvania and the Corporal Michael J. Crescenz VA Medical Center.

Data Analysis
To compare the associations between suicide risk and physical, psychological, social and military factors, we conducted a binary logistic regression
analysis with suicide risk as the outcome and a set of 29 predictor variables. We retained, in the models, predictor variables for which p < 0.20 in univariablelogistic regression models. Although age, marital status, race, LOC and total number of TBIs were not significant in the univariable models, they were retained as control variables due to their theoretical importance.

Results
Demographic characteristics are presented in Table 1. All participants were male, between 29 and 79 years old (M = 53.73, SD = 7.07) and approximately half had been married at some point in their lifetime (52.4%, n = 55). Most participants identified as nonwhite (82.5%, n = 85). Depression was reported in 17.5% (n = 18) of the sample, anxiety in 9.7% (n = 10), bipolar disorder in 2.9% (n = 3), psychotic disorder
in 7.8% (n = 8), and PTSD in 21.4% (n = 22). Alcohol abuse was reported in 32.0% (n = 33) of the sample and substance abuse, other than alcohol, was reported in 50.5% (n = 52). Approximately one-third (n = 39) had been deployed at least once and 14.6% (n = 15) had combat experience. Approximately twothirds (63.1%, n = 65) of the sample had 3 or more TBIs, with 82.5% (n = 85) reporting accompanying LOC. Veterans who reported high risk of suicide also reported significantly more frequently that they experienced the following TBI-related symptoms: blurred vision, seizures and difficulty with memory/ problem-solving and managing stress.

Discussion
The present study is the first to assess the relationship between factors related to suicide risk among a sample of veterans experiencing both homelessness and TBI. The findings presented are particularly important given the high rates of TBI, suicide and homelessness among the veteran population. This study indicated that, although veterans reporting low-to-moderate risk of suicide are demographically similar to those experiencing high risk—and have suffered approximately the same number of TBIs— their reporting of post-TBI symptoms are significantly different. Veterans expressing high risk of suicide more frequently experienced blurred vision, difficulty managing stress, struggles with memory and problem-solving and seizures following a TBI; the presence of these symptoms may be an indication of a more severe TBI or rTBI which has been associated
with increased risk of suicide. In addition, these veterans also more frequently reported symptoms consistent with PTSD which overlap to a large degree with symptoms of TBI.

This study found that veterans with PTSD had 8 times the odds of being at high risk for suicide, compared with those who did not have PTSD. Several
other studies have identified a similar relationship between PTSD and suicide among veterans. Veterans experiencing homelessness who have PTSD may be at greater risk for suicide than non-homeless veterans for a number of reasons: they may have limited access to appropriate mental health resources given a lack of sustainable income or health insurance; they are faced daily with stressful situations that can trigger or exacerbate PTSD symptoms, such as lack of food and shelter or unsafe conditions; or they may be struggling with alcohol and substance abuse which may worsen PTSD symptoms10.

The interpretation of study findings must be tempered by a number of study limitations. First, the sample was quite small, fairly homogeneous,
and likely represented the setting from which it was drawn, limiting the ability to generalise to the larger population of veterans experiencing homelessness. Second, due to limitations of data collection instruments used for this study, the present analyses could not control for a number of variables including severity of the TBI and PTSD, whether these were the result of injuries incurred during combat and if symptoms reported by veterans were due to TBI, PTSD or some other condition. Third, the identification of marriage status as a predictor of suicide risk should be tempered by the fact that approximately half the sample was married, potentially biasing the results. Future studies should consider using administrative
data, at the population level, supplemented with additional primary data related to the circumstances surrounding veterans’ TBIs and experience of
combat.